1. Field of the Invention
The present invention relates to an integrated circuit for an image pickup device, where the integrated circuit is to be used for driving an image pickup apparatus or for the signal processing of picture signals obtained from the image pickup apparatus, and more particularly to a reduction in the power dissipation of the image pickup apparatus.
2. Description of the Related Art
In order to miniaturize various portable equipment, a smaller sized battery is also used for loading into the equipment. Lower power dissipation is also designed so that a sufficient operating time is possible with a small battery of small capacity. In like manner, low power dissipation and compact size are desirable features in digital still cameras and video cameras. Furthermore, as the communication capacity has expanded in recent years, it has become possible for cellular phones and portable terminals to handle graphics, and it has become desirable for these equipments to include an image pickup function. These cellular phones are becoming more compact and require a further reduction in power dissipation.
Heretofore, a reduction in the driving voltage for CCD (Charge Coupled Device) image sensors or in the driving voltage for analog signal processing circuits for processing the output signal of image sensors were designed, and further a standby function was employed. Incidentally, the standby function is assumed to be a state in which the drive operation of the main circuitry for image pickup is stopped during a period where image pickup is not performed, even if the main power switch is in the on state. For example, the image pickup in a digital still camera is basically performed on an intermittent basis. In this case, the interval period between image pickup operations is long so that a larger effect in the reduction of power dissipation can be obtained from the standby function. Furthermore, in particular, unlike the digital signal processing circuit, an analog signal processing circuit requires a steady current during operation and the power dissipation is large, thereby making the standby function effective.
Although several techniques have been adopted in the past as described above to lower the power dissipation, the further lowering of power dissipation has become a technical problem.